Hill Start in a Vehicle

ABSTRACT

A hill brake system in a vehicle uses a controller to determine when a number of conditions, such as being stopped on an incline, are met and then automatically applies a braking force at least equal to a calculated grade load, that is, gravitational force. Using drive train measurements and known drivetrain characteristics, a rimpull force is calculated after release of an operator-controlled brake and the automatically applied braking force is reduced corresponding to the rimpull force generated by the drivetrain. The automatically applied braking force is released when any of several conditions are met including uphill motion of the vehicle or expiration of a timeout timer.

TECHNICAL FIELD

The present disclosure relates to an automated braking system for use inpreventing downhill motion when starting a vehicle on an incline.

BACKGROUND

Heavy equipment, such as large earthmoving vehicles, must often stop oninclines. However, restarting from an incline may cause a challenge foran operator wishing to avoid rolling downhill while accelerating fromthe stopped position. In many cases, the operator will “two foot” theprocess, applying the left foot to the brake and the right foot to theaccelerator so that the engine torque increases to a point wherereleasing the brake will not cause downhill motion.

This process, however, has several drawbacks. Unintended motion downhillis one. The two foot operation, in addition to simply being a nuisanceor a distraction to the operator, causes the brakes to be applied overincreasing engine torque and may cause undue wear on the brakes, as wellas undue wear on drive train components such as a torque converter,gearbox, and/or drive motors.

EP1581418 to Lauri, discloses a hill brake system that selects asuitable starting gear and determines a minimum torque and engine speedrequired to overcome a traveling resistance of the vehicle and thenreleases a clutch and the brake as the minimum engine speed and torqueare achieved. Lauri, however fails to disclose determining deliveredrimpull force at a drive wheel of the vehicle and reducing a brakingforce proportional to the rimpull.

SUMMARY OF THE DISCLOSURE

In a first aspect, a method of providing a hill brake in a vehicleincludes applying a braking force required to prevent the vehicle fromrolling in a downhill direction after an operator-controlled brake isreleased, calculating a rimpull at a drive wheel of the vehicle, andreducing the braking force as the rimpull increases.

In another aspect, a controller that provides a hill brake in a vehicleon an incline during acceleration from a stop includes a rimpullsubsystem that determines force at a drive wheel of the vehicle, a gradeload subsystem that determines a downhill force on the vehicle, abraking subsystem that supplies a braking force sufficient to preventdownhill motion of the vehicle, wherein the braking force decreasescorresponding to an increase in force at the drive wheel.

A method of providing a hill brake in a vehicle may include determiningthat the vehicle is on an incline, determining that the vehicle isstopped, determining that the vehicle is configured for uphillpropulsion, and calculating a grade load on the vehicle. The method mayalso include calculating a braking force approximately equal to thegrade load, applying the braking force via a braking system in thevehicle, and sensing release of a brake pedal. The method may continueafter sensing release of the brake pedal and until a trigger event isreached by calculating a rimpull at a drive wheel of the vehicle,reducing the braking force corresponding to an increase in rimpull, andupon reaching the trigger event, releasing the braking force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a vehicle on an incline;

FIG. 2 is a simplified schematic diagram of the vehicle of FIG. 1showing components associated with a hill brake system;

FIG. 3 is a block diagram of an exemplary controller operative in thehill brake system; and

FIG. 4 is a flow chart of an exemplary method of providing hill start ina vehicle.

DETAILED DESCRIPTION

FIG. 1 is an illustration of a work site 100 showing a vehicle 102 on anincline 104. The incline 104 may be measured by an angle θ 106 from alevel reference 108. In the illustration, the vehicle 102 is shownfacing uphill, that is so that driving in a forward gear causes uphillmotion. When discussing a hill brake, it is equally valid that thevehicle 102 may be facing downhill such that driving in a reverse gearcauses uphill motion.

FIG. 2 is a simplified schematic diagram of the vehicle 102 of FIG. 1showing components associated with a hill brake system. The vehicle 102may include an engine 122, coupled to a torque converter 124, whoseoutput drives a transmission 126 and ultimately delivers torque via anaxle 128 to drive wheels 130.

In an embodiment, wheels 132 may be unpowered and may carry a payloadbearing element of the vehicle 102. For example, the vehicle 102 may bean articulated truck. In other embodiments, the vehicle 102 may be anyof a number of machines including, but not limited to, earthmovers, dumptrucks, mining equipment, etc. In these other embodiments, the exactarrangement of drive train and drive wheels 130 may differ from thatdescribed with respect to the exemplary embodiment discussed here indetail.

The wheels 132 may be connected by respective axles 134. The controller136 may be coupled via a sense line or lines 138 to the torque converter124. The controller 136 may also receive a current gear selection fromthe transmission 126 via a sense line 139. A sensor 140 may report axlespeed and/or ground speed to the controller 136. An inclinometer 142 mayreport vehicle angle to the controller 136. The inclinometer 142 mayreport vehicle angle both front-to-back and side-to-side as well aspositive or negative front-to-back angles depending on the orientationof the vehicle 102 with respect to the incline 104. A load sensor 143may report a weight of the payload of the vehicle 102 or some valueassociated with the payload weight, such as readings from strain gauges,etc. In an embodiment, the payload may be determined using otherinstruments, such as an accelerometer.

The controller 136 may provide a control current to a drive wheel brakevalve 144 and an unpowered wheel brake valve 146 via an electricalconnection 148. Other embodiments, for example, those using a differentbraking mechanism, may use a different control mechanism for applyingbraking force. For example, if the brake being used is a driveline brakeand not a hydraulically operated wheel disk or rotor brake, a differentcontrol scheme may be implemented in keeping with the currentdisclosure. The respective brake valves 144 and 146 may increasepressure in brake lines 150 to cause application of brakes (notdepicted) to transmit a braking force to the wheels 130, 132. Note thatthe hill brake itself is not a single, standalone mechanism. The hillbrake is a combination of sensors and existing braking mechanismsoperated at the direction of the controller 136 under a very limited setof vehicle operating conditions.

The embodiment illustrated in FIG. 2 is an engine/torqueconverter/transmission drivetrain. In another embodiment, the drivetrainmay be a generator/electric motor set that may include one more electricpower inverters, batteries, and/or reduction gears. In the discussionthat follows, the nature of the drivetrain is relevant to the extentthat a determination of rimpull is available.

FIG. 3 is a block diagram of an exemplary controller 136 operative toprovide hill braking. The controller 136 may include a processor 170, amemory 172 and a data bus 174 that communicates information betweenphysical elements of the controller 136. The controller 136 may includea communication port 176 that supports data communication with an enginecomputer or other equipment, such as operator station electronics, via avehicle network 178. The controller 136 may also include a sensor inputcircuit 180 that may receive data from, for example, the axle and/orgroundspeed sensor 140, the inclinometer 142, and the load sensor 143.The controller 136 may also include a brake output circuit 182 thatprovides a drive current to the brake valves 144 and 146.

The memory 172 may be a physical memory including volatile and/ornonvolatile physical memory including but not limited to RAM, ROM,programmable arrays, flash memory, etc. The controller 136 may includean operating system 184, such as a real-time operating system (RTOS) orother known operating system, utilities 186 that may support routinefunctions such as communication via the communication port 176,diagnostics, etc.

The memory 172 may also include a hill brake application 188 thatoperates to provide hill braking as described. The hill brakeapplication 188 may include a rimpull subsystem 190, a grade loadsubsystem 192, a braking subsystem 194, a math subsystem 196, andvarious constants or lookup tables 198. In an embodiment, the mathsubsystem 196 may be a proportional controller.

The controller 136 may be a standalone unit as depicted, or may beincluded as a function in a different physical computer-orientedprocessor or engine controller (not depicted). Other embodiments of astandalone controller, the actual functions may be implemented in adifferent manner, such as a field programmable gate array or the use ofdifferent specific subsystem combinations that achieve a functionalequivalent.

INDUSTRIAL APPLICABILITY

In general, the ability to provide a hill brake for a vehicle 102increases both site safety and operator satisfaction. Because, for atleast a limited period of time, the vehicle 102 is not in danger ofrolling downhill there is a reduced threat to personnel, other vehicles,or obstructions that may be downhill of the vehicle 102. Further, anoperator may be able to release the foot brake and apply the throttle inan orderly manner without undue worry regarding timing of the brake andthrottle operation and as a result may both reduce operator stress andthe reduce the risk of damage to the brakes or drivetrain. As a result,the operator may be able to increase his or her attention to thesurrounding work area and note potential safety hazards associated withmoving the vehicle 102. Using rimpull as a measure of available forceincreases the accuracy of the calculation of braking force required tooffset grade load and may allow more accurate release of the brakingforce during operation of the hill brake.

FIG. 4 is a flow chart of an exemplary method 200 of providing hillstart in a vehicle 102. At block 202, various information about thevehicle, including torque converter constants, gear ratios of thetransmission 126, and wheel characteristics may be provided. Forexample, for a given torque converter 124, the ratio of input speed tooutput speed often predicts an output torque with a high degree ofaccuracy.

At block 204, vehicle conditions may be evaluated to determine if hillbrake operation is appropriate. For example, the vehicle 102 should beon an incline. If the vehicle 102 is on flat ground there is norequirement for use of the hill brake. To determine if the vehicle 102is on an incline 104, an inclinometer 142 may be used. In an embodiment,if the incline 104 is less than a few percent, the hill brake may alsobe disabled. A determination may also be made that the vehicle 102 is infact stopped as the use of the hill brake is not indicated while thevehicle 102 is still in motion.

A determination may be made that the vehicle 102 is in an uphill gear.For example, if the vehicle 102 is facing uphill, a forward gear must beengaged. On the other hand, if the vehicle 102 is facing downhill, areverse gear must be engaged. Last, a foot brake or otheroperator-activated brake must be applied. There is no intent for thehill brake to operate over a long period as a parking brake.

At block 206, the grade load may be determined by developing the weightof the payload using a load sensor 143, adding the known or estimatedweight of the vehicle 102 and multiplying the result by the sine of theangle of incline θ 106. Estimated vehicle weight may include fuel weightbased on fuel tank level sensing and the density of the fuel. The gradeload represents the amount of downhill force that must be overcome bythe brakes to prevent downhill movement of the vehicle 102.

At block 208, the amount of braking force required to equal, or in anembodiment, slightly surpass the grade load is used to calculate anamount of braking pressure required to yield the necessary brakingforce. For a given vehicle 102, the braking pressure, that is, theamount of pressure on brake fluid in the brake lines 150 may becorrelated to the amount of braking force applied at the brakes. In anembodiment, a table of braking force to braking pressure may bedeveloped and stored in the memory 172, for example in the constants andtables 198.

At block 210, the required braking pressure may be applied via a signalfrom the controller 136 to the brake valves 144 and 146. In variousembodiments, the braking pressure may be applied before release of thefoot pedal or other operator activated braking mechanism, or may beapplied concurrently with release of the foot pedal or other operatoractivated braking mechanism. In an embodiment, braking force may beincreased slightly over the minimum calculated in order to account forcomponent wear or sensor inaccuracies.

At block 212, release of the foot pedal or other operator activatedbraking mechanism may trigger actual operation of the hill brake.

At block 214, an evaluation may be made regarding the occurrence of oneor more trigger events related to exit from the hill brake operatingmode. For the purpose of illustration it will be assumed that theinitial entry to block 214 occurs prior to any trigger event and the‘no’ branch is taken from block 214 to block 216.

At block 216, rimpull, that is, force applied at the ground by the drivewheels 130 may be calculated using drivetrain torque information. Forexample, input and output speed at the torque converter 124 incombination with the known forward or reverse gear at the transmission126 may be used to develop axle torque at the drive wheels 130. Usingknown size information for the wheels 130 the axle torque may beconverted to rimpull. For example, the newton-meters of axle torque canbe converted to rimpull using the size difference between the axle andthe outside diameter of the wheel using the simple equationtorque=force×distance. A known rolling resistance of the vehicle may besubtracted from the rimpull.

In the case of an electric motor drivetrain, motor torque may bemeasured using a torque sensor or may be calculated using, for example,a flux calculation and measured current. As discussed above, rimpull maythen be calculated using the motor torque, any intervening gearing, andwheel characteristics.

At block 218, the amount of rimpull may be subtracted from the gradeload to develop a new braking force requirement. As above, the brakingforce requirement may be translated to a braking pressure andsubsequently the controller 136 may adjust the control current to thebrake valves 144 and 146 to reduce the braking pressure as calculated.The braking force may be reduced proportional to the increase inrimpull. For example, braking force may be reduced linearly as afunction of grade load force—rimpull. In another embodiment, the brakingforce may be reduced exponentially so that as rimpull graduallyincreases the braking force may be reduced only a small amount and asrimpull approaches grade load, the braking force is reduced morequickly. Execution may continue at block 214.

Returning to block 214, a number of trigger events may be evaluated todetermine whether to repeat the loop. First, a timer may be checked todetermine if a timeout period has expired related to an amount of timethe hill brake function has been active that is, from the release of thebrake by the operator at block 212 to the current time. As mentionedabove, the goal is not to use the hill brake as a parking braketherefore a limit on how long the hill brake is active may be set to arelatively short period of time, such 1 to 3 seconds. In an embodimentwhere the timeout period is two seconds, the operator is givensufficient time to activate the throttle and increase the torque of theengine 122 but is not given enough time to stand up and exit the cabbefore an alarm sounds and/or the brake is released. Alternatively, anoperator may desire to roll downhill in some cases and the relativelyshort timeout period allows such operation without undue interruption.

A second trigger event may be one the rimpull is greater than the gradeload. At this point, braking force is no longer required and the brakingforce may be reduced to zero by appropriate reductions in brakingpressure.

A third trigger event may be actual uphill movement of the vehicle 102using information from an axle or groundspeed sensor 140.

A fourth trigger event may be uphill rotation of one or more drivewheels 130 using information from the axle or groundspeed sensor 140.

Upon occurrence of any of the trigger events, the ‘yes’ branch may betaken from block 214 to block 220 where the brakes are released via achange in control current from the controller 136 to the brake valves144 and 146.

Execution may continue at block 204 to determine when it may beappropriate to reactivate the hill braking function.

What is claimed is:
 1. A method of providing a hill brake in a vehiclecomprising: applying a braking force required to prevent the vehiclefrom rolling in a downhill direction after an operator-controlled brakeis released; calculating a rimpull at a drive wheel of the vehicle; andreducing the braking force as the rimpull increases.
 2. The method ofclaim 1, wherein reducing the braking force comprises removing thebraking force after detection of a trigger event.
 3. The method of claim2, wherein the trigger event is one of an uphill motion of the vehicleand an uphill rotation of the drive wheel.
 4. The method of claim 2,wherein the trigger event is expiration of a timeout period measuredfrom a time the operator-controlled brake is released.
 5. The method ofclaim 1, where calculating rimpull comprises: determining torque at anoutput of a torque converter; determining a current gear setting;calculating axle torque from the output power and a gear ratio of thecurrent gear setting; and calculating rimpull using a known conversionof axle torque to rimpull force less a known rolling resistance.
 6. Acontroller that provides a hill brake in a vehicle on an incline duringacceleration from a stop, the controller comprising: a rimpull subsystemthat determines force at a drive wheel of the vehicle; a grade loadsubsystem that determines a downhill force on the vehicle; and a brakingsubsystem that supplies a braking force sufficient to prevent downhillmotion of the vehicle, wherein the braking force decreases correspondingto an increase in force at the drive wheel.
 7. The controller of claim6, wherein the braking subsystem comprises: an output driver thatapplies an electrical current to a braking control valve that generatesa braking pressure corresponding to the electrical current to provide abraking pressure sufficient to generate the required braking force. 8.The controller of claim 7, further comprising a calculation functionthat receives the downhill force from the grade load subsystem,determines a required braking force to offset the downhill force, andreports the required braking force to the braking subsystem.
 9. Thecontroller of claim 6, wherein the rimpull subsystem, to determine forceat the drive wheel, determines torque at an output of a torqueconverter, determines a current gear setting to calculate axle torqueand a gear ratio of the current gear setting and calculates rimpullusing a known conversion of axle torque to rimpull force less rollingresistance.
 10. The controller of claim 6, wherein the grade loadsubsystem includes: a first input that receives data used to calculatean angle of the vehicle; a second input that receives a signalcorresponding to payload weight; and a calculation function that adds avehicle weight to the payload weight and calculates the downhill forceon the vehicle using the data from the inclinometer.
 11. A method ofproviding a hill brake in a vehicle comprising: determining that thevehicle is on an incline; determining that the vehicle is stopped;determining that the vehicle is configured for uphill propulsion;calculating a grade load on the vehicle; calculating a braking forceapproximately equal to the grade load; applying the braking force via abraking system in the vehicle; sensing release of a brake pedal; aftersensing release of the brake pedal and until a trigger event is reached:calculating a rimpull at a drive wheel of the vehicle; and reducing thebraking force corresponding to an increase in rimpull; and upon reachingthe trigger event, releasing the braking force.
 12. The method of claim11, wherein the trigger event is expiration of a timeout period.
 13. Themethod of claim 11, wherein the trigger event is the rimpull greaterthan the grade load.
 14. The method of claim 11, wherein the triggerevent is uphill motion of the vehicle.
 15. The method of claim 11,wherein the trigger event is uphill rotation of the drive wheel.
 16. Themethod of claim 11, wherein calculating the grade load comprises:determining a payload weight; adding the payload to a known vehicleweight to develop a gross vehicle weight; determining a vehicle angle;and computing the grade load as a mathematical function of the vehicleangle and the gross vehicle weight.
 17. The method of claim 11, furthercomprising: converting the required braking force to a braking pressurerequired to generate the required braking force using a predeterminedmapping function; and applying the braking pressure.
 18. The method ofclaim 17, wherein applying the braking pressure comprises activating abrake control valve with an electrical current value corresponding tothe required braking pressure.
 19. The method of claim 11, whereincalculating the rimpull comprises: measuring electrical motor torque;and converting the electrical motor torque to rimpull using drivetrainand wheel characteristics.
 20. The method of claim 11, wherein reducingthe braking pressure corresponding to the rimpull comprises adjustingthe braking force to be approximately equal to the grade load minus therimpull.